<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
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    <title>Document</title>
    <style>
        p:nth-child(2n){
            color: red;
        }
    </style>

</head>
<body>
     <p>我是文本1</p>
     <p>
         <P>我是文本2</P>
         <P>我是文本3</P>
     </p>
     <p>我是文本4</p>
     <p>我是文本5</p>
     <p>我是文本6</p>
</body>
</html>